2.1 Field of Invention
This invention is a novel method for perfusion of a porous implant which achieves efficient interpenetration of desired factors into the pores or channels of the implant, cleaning of the implant, efficient passivation of the implant (inactivation of pathogens, microorganisms, cells, viruses and the like and reduction in antigenicity thereof), and the novel implant produced by such treatment.
2.2 Description of Known Procedures for Implant Treatment
As used in this disclosure, the term “implant” refers to any material the implantation of which into a human or an animal is considered to be beneficial. Accordingly, the implant may be tissue-derived material, such as bone, skin, and the like, or it may be a metallic or synthetic material having an internal structure that may require cleaning or sterilization. Bearing this definition in mind, it will be apparent that many procedures have been described in the art for treatment of implants to either clean such implant, inactivate contaminating microorganisms or cells that may be present in, or on such implant, or to infuse the implant with desirable factors. This section of the disclosure discusses several known methods for achieving one or more of these results, in order to more clearly and definitively set forth that which has been invented, and which is disclosed and claimed as novel and inventive, as defined by the claims appended hereto.
European Patent Application No. EP 0 424 159 (Osteotech)—“Aseptic Processing of Allograft Bone and Tissue,” (published Apr. 24, 1991, based on a U.S. Priority application filed Oct. 19, 1989), it an extremely general disclosure relating to aseptic processing of allograft bone and tissue. It appears that the intent of this application was to establish an early priority date in an effort to foreclose the entire field of aseptic processing of allograft bone and tissue. However, the disclosure is so general that it does not appear to contain an enabling disclosure of any protectible allograft sterilization method. No U.S. or European patent related to this extremely general published application appears to have ever issued.
In U.S. Pat. No. 5,333,626 (Cryolife)—“Preparation of Bone for Transplantation”, (issued on Aug. 2, 1994, based on an application filed on Dec. 31, 1991), relates to a method of preparing bone for transplantation by maintaining the internal matrix of the bone to be implanted, preferably at high pressure, in the presence of a decontaminating agent, preferably polyvinyl pyrrolidine-iodine (PVP-I) optionally in the presence of a detergent, in,solution. The “high pressure” feature of this patent is described at column 5, lines 10-31: “High pressure washing conditions should provide a force sufficient to drive the cleaning solution into internal matrix of the bone. Such high pressure washing conditions include, for example, vigorous agitation, such as with a paint can shaker, or high pressure lavage such as with a high pressure liquid jet stream. The pressure of the liquid jet stream is preferably 100 to 3,000 psi and most preferably 500 to 1,500 psi.” However, the patent does not disclose or suggest exposure of an implant to an oscillating atmospheric pressure, the referenced patent requires pressures significantly higher than those required according to the present invention, and it is only applicable to bone, while the present invention is applicable to bone or soft tissue. In addition, the claimed process requires approximately 1-2 days to complete.
In U.S. Pat. No. 5,513,662 (Osteotech)—“Preparation of Bone for Transplantation” (this patent issued on May 7, 1996 as a continuation-in-part of the application that issued as the U.S. Pat. No. 5,333,626 patent, based on an application filed on Jan. 21, 1994, and claiming priority to the Dec. 31, 1991 filing date of the application on which the U.S. Pat. No. 5,333,626 patent is based), relates to a method of preparing bone for transplantation in which the internal matrix of the bone is maintained at a pressure below one atmosphere. It is disclosed (column 10, lines 13-19) that “optimum times for maintaining pressure below ambient are generally in the range of 30 to 60 minutes but can be determined for each application by monitoring progress of blood and lipid extraction (see Example 10).” It is further disclosed that generally use of gas pressure below ambient for less than two minutes will be ineffective and use for longer than five hours will confer no further benefit. Thus, the '662 patent requires that the bone be maintained for substantial periods of time at pressures below one atmosphere. There is no disclosure or suggestion of rapidly cycling between elevated and decreased pressures, even though it is suggested that the bone might first be treated at an elevated pressure, followed by a treatment step at a pressure below atmospheric pressure (see, for example, claim 3, column 15). The present invention discloses a process wherein transient and cyclical exposure of an implant material to a given pressure achieves the desired result of implant cleaning, perfusion or passivation.
In U.S. Pat. No. 5,556,379 (LifeNet Research Foundation)—“Process for Cleaning Large Bone Grafts and Bone Grafts Produced Thereby,” (issued on Sep. 17, 1996 based on an application filed on Feb. 27, 1995, and claiming priority of an earlier, abandoned application, filed Aug. 19, 1994), describes the “Allowash™” process. The patent is explicitly directed to the removal of “bone marrow from the luminal and cancellous bone spaces in large, essentially whole, bone grafts.” (See Summary of the Invention). Accordingly, the referenced patent is directed only to treatment of bone; which has to be largely intact. The stated intent in applying the process to essentially whole bone grafts is to reduce the load of potentially virus carrying bone marrow to facilitate preparation of smaller bone grafts therefrom. The process involves applying a vacuum to the bone graft to draw solution capable of solubilizing bone marrow through articulating cartilaginous surfaces and through the intact bone's intramedullary canal or other bone cavity. The patent neither discloses nor suggests a method in which oscillating pressures are used to clean a bone graft.
U.S. Pat. No. 5,380,826 (Aphios Corporation)—“Supercritical Fluid Disruption of and Extraction from Microbial Cells, (issued on Jan. 10, 1995, based on an application filed on Sep. 29, 1992), relates to a method for harvesting intracellular components by exposing cells to an elevated pressure in the presence of a solvent, and then rapidly and suddenly releasing the pressure to effect disruption of the cells. The patent also discloses an apparatus for carrying out this process continuously. However, this patent neither discloses nor suggests applying the cell disruption method to allograft bone.
U.S. Pat. No. 5,288,462 (Stephen D. Carter)—“Sterilization Apparatus and Method” (issued on Feb. 22, 1994, based on an application filed on May 18, 1992), describes a chamber for receiving a material to be sterilized by repeatedly subjecting the chamber to elevated pressures, followed by sudden release of the pressure, i.e. “explosive decompression.” The patent requires that the chamber be pressurized to at least 1000 psi. The patent neither discloses, suggests, nor claims application of this method or chamber to sterilization of bone materials. There is no disclosure of cleaning solutions used in connection with the described apparatus that would be effective in sterilizing the matrix of a bone. There is no disclosure that would allow one skilled in the art to determine, without undue experimentation, that bone could be sterilized in this apparatus. In addition, there is no disclosure nor suggestion that an implant could be sterilized without use of such highly elevated pressures, but merely by oscillation of lower absolute pressures.
U.S. Pat. No. 5,725,579 (Bioland)—“Process for Treating Bone Tissue and corresponding Implantable Biomaterials”, (issued Mar. 10, 1998, based on a priority French application filed Dec. 21, 1992 and an earlier U.S. priority filing of Dec. 9, 1993), is directed to a method of cleaning bone by exposing the bone to a supercritical fluid. As best as can be understood from this patent, this involves exposing bone to carbon dioxide at elevated pressures, in order to solubilize lipids.
Tissue sterilization methods known in the art have undesirable attributes. Gamma irradiation, in order, to ensure destruction of pathogens, such as the human immunodeficiency virus (HIV), has to be used at doses that result in tissue destruction (e.g. 3.5. Mrad; see, for example, Rasmussen, et al., J. Arthroscopic and Related Surgery, 10(2):188-197, (1994); Goertzen, et al., British Soc. of Bone and Joint Surg., 77:204-211 (1005); Loty, et al., International Orthopaedics, 14:237-242, (1990)). Use of ethylene oxide has been found to result in implants that produce inflammatory responses (Kudryk, et al., J. Biomedical Materials, 26:1477-1488, (1992); Thoren, et al., Clin. Orthopaedics, 318:259-263, (1995); Simonian, et al., Clin. Orthopaedics, 302:290-296, (1994); Jackson, et al., Am. J. Sports Medicine, 18:1-9, (1990)). Standard chemical solution treatments, while effective in sterilizing surfaces with which the solutions are brought into contact, have the major disadvantage of being insufficiently penetrating to reach the interstices of tissues, where potentially pathogenic organisms may reside. In view of these shortcomings, there remains a long-felt-need for an optimized tissue sterilization process, which would incorporate some or all of the following features: Effective removal or inactivation of a wide range of bacterial and viral pathogens; absence of graft toxicity; retention of desirable tissue characteristics, such as biomechanical strength or growth-inducing properties; effectiveness across a wide range of operating modifications and for a wide variety of tissue types; ability to conclude the process in a final implant tissue container, to ensure sterile packaging and delivery for implantation.
In view of the foregoing review of the known art relating to implant treatment and sterilization methods, it is believed that the present invention provides a long needed improvement in that no absolute temperatures or pressures are required to achieve efficient implant cleaning, perfusion, or passivation. In addition, the instant method does not require drilling of holes in implant materials or any other manipulation or modification in order to achieve efficient implant cleaning and sterilization. Furthermore, the present method permits safe pooling of donor tissue for implant production at economies of scale, without at the same time diminishing the desirable biological properties of the pooled implant materials. The instant process includes a number of methodologies, the additive effect of which is the production of highly cleansed, sterilized (passivated) tissues, which may be implanted, without causing toxicity to the recipient. Various embodiments of the method of this invention includes all of the above listed features, namely: effective removal or inactivation of a wide range of bacterial and viral pathogens; absence of graft toxicity; retention of desirable tissue characteristics, such as biomechanical strength or growth-inducing properties; effectiveness across a wide range of operating modifications and for a wide variety of tissue types; ability to conclude the process in a final implant tissue container, to ensure sterile packaging and delivery for implantation.